1. Field of the Invention
The present invention relates to a process for continuously producing 2,2-bis(4-hydroxyphenyl)propane ("p,p'-BPA" hereinbelow) having a high quality from a reaction of phenol and acetone in the presence of a hydrochloric acid catalyst. More specifically, it relates to a process for continuously and economically producing p,p'-BPA having a high quality at a high yield to the reacted phenol and acetone.
2. Description of the Prior Art
p,p'-BPA has heretofore been used as a starting material for the production of polycarbonate or epoxy resins. Recently, the high quality resins have been coming into increased demand and have been used for a wider range of applications. As a result, higher quality resins have been required in the art. Along with this, a higher quality product of p,p'-BPA having a high purity and good color has come into demand as a starting material of these resins. Especially, a high quality p,p'-BPA having, for example, a purity of 99.9 mole % or more and APHA color of a molten product of 30 or less has been demanded as a starting material for polycarbonate. Furthermore, it is also required to economically produce a high quality p,p'-BPA. In order to fulfill these requirements, it is necessary to selectively produce p,p'-BPA by reacting starting phenol and acetone at a high one-pass conversion.
Furthermore, the resultant p,p'-BPA should be readily purified and a high quality p,p'-BPA should be produced at a high yield and low cost. More specifically, when the starting phenol and acetone are reacted in the presence of an acid catalyst, various by-products are also produced in addition to the desired p,p'-BPA. Examples of such by-products are isomeric by-products such as 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane ("o,p'-BPA" hereinbelow) and 2,2-bis(2-hydroxyphenyl)propane ("o,o'-BPA" hereinbelow); high boiling point by-products such as 4-(4-hydroxyphenyl)-2,2,4-trimethylchroman ("co-dimer" hereinbelow), 2,4-bis(.alpha.,.alpha.-dimethyl-4-hydroxybenzyl)phenol ("BPX" hereinbelow), 2-(2-hydroxyphenyl)-2,4,4-trimethylchroman ("o-dimer" hereinbelow), 5-hydroxy-3-(4-hydroxyphenyl)-1,3,3-trimethylindane ("IPEP cyclic dimer" hereinbelow), and 2,4-bis(4-hydroxyphenyl)-4-methyl-1-pentene ("IPEP linear dimer" hereinbelow); and other colored unknown structure by-products. Therefore, those by-products capable of being converted to p,p'-BPA must be readily and efficiently converted to p,p'-BPA.
Heretofore, many processes for producing p,p'-BPA by reacting phenol and acetone in the presence of an acidic catalyst have been proposed. For example, the use of hydrogen chloride or hydrochloric acid as a catalyst in the reaction of phenol and acetone and the purification and separation of the desired p,p'-BPA from the resultant reaction product derived from the above-mentioned reaction are disclosed in, for example, Japanese Examined Patent Publication Nos. 27-5367, 36-23335, 38-4875, 40-7186, 42-6333, 43-3379, 47-10384, and 50-12428 and Japanese Unexamined Patent Publication Nos. 48-97853, 49-93347, 49-82651, 53-101347, 54-98748, and 54-98749.
However, these proposed processes have had problems in that a large amount of the above-mentioned by-products including isomeric by-products, high-boiling point by-products, and colored by-products are formed when p,p'-BPA is produced according to the processes disclosed in the above-mentioned publications. The formation of the by-products decreases the selectivity of the reaction to the desired p,p'-BPA. Furthermore, the quality of the desired product is decreased and the purification of the desired product becomes difficult due to the contamination thereof with the by-products. Consequently, the desired p,p'-BPA having a high quality cannot be economically produced at a high yield and a high selectivity according to the above-mentioned prosesses. Furthermore, when the purification and separation methods disclosed in the above-mentioned publications are used for treating the reaction mixture obtained from the above-mentioned catalytic reaction, the removal of the above-mentioned by-products is difficult. Therefore, high-quality p,p'-BPA cannot be selectively and economically produced at a high yield.
For example, of the above-mentioned prior publications in which the intended reaction are carried out in the presence of hydrogen chloride or hydrochloric acid as a catalyst, Japanese Examined Patent Publication No. 42-6333 proposes a process for the production of p,p'-BPA from phenol and acetone in which p,p'-BPA is recovered from the by-products (i.e., resinous by-products) after removing p,p'-BPA from the reaction product of phenol and acetone. The by-products and phenol are treated in the presence of hydrogen chloride or hydrochloric acid to improve the substantial selectivity of the reactants to p,p'-BPA and the yield of p,p'-BPA and, then, the resultant p,p'-BPA is recovered from the reaction mixture. However, according to this proposed process, the p,p'-BPA is first separated from the reaction mixture obtained by the reaction of phenol and acetone in the presence of hydrogen chloride or hydrochloric acid. The treatment of the by-products thus obtained and the condensation reaction of acetone and phenol are also carried out in separate reactors according to the above-mentioned process. This complicates the reaction systems and, further, increases the amounts of the by-products to be treated in the isomerization reaction. Since the isomerization reaction of the by-products into the desired p,p'-BPA is limited to the equilibrium composition, the isomerization efficiency of the by-products into p,p'-BPA becomes low. Consequently, the overall selectivity to the desired p,p'-BPA and the overall yield of the desired p,p'-BPA are low and the desired p,p'-BPA cannot be economically produced.
Furthermore, of the above-mentioned prior publications disclosing the use of hydrogen chloride or hydrochloric acid in the preparation reaction of p,p'-BPA, Japanese Examined Patent Publication No. 42-26787 discloses a process for producing p,p'-BPA having a high purity from a mixture obtained by removing hydrogen chloride from the reaction mixture after the completion of the reaction. According to this process, hydrogen chloride gas is removed from the reaction mixture by treating the reaction mixture under a reduced pressure (or in vacuo) without heating or bubbling an inert gas into the reaction mixture and, then, the phenol adduct of p,p'-BPA ("p,p'-BPA.PhOH" hereinbelow) is crystallized from the resultant mixture, followed by the decomposition of the p,p'-BPA.PhOH. Thus, p,p'-BPA is recovered.
In a specific embodiment thereof, it is described that the reaction mother liquor separated from the p,p'-BPA.PhOH by filtration can be circulated to and used in the reactor. However, this process is still disadvantageous in that p,p'-BPA having a high purity cannot be economically produced. That is, the formation of hydrochloric acid should be suppressed in the reaction system in order to effectively remove the hydrogen chloride from the reaction mixture and, therefore, as is clear from the examples of the above-mentioned publication, the conversion of the starting acetone in the reaction should be maintained to as low as about 50% or less to minimize the amount of water formed by the reaction and the effective reutilization of the hydrogen chloride is substantially difficult even if the reaction mother liquid is recycled since the substantial amount of the hydrogen chloride gas is removed from the reaction mother liquor.
In addition, the comparative tests in Example 1 of Japanese Examined Patent Publication No. 42-26787 discloses that p,p'-BPA is recovered from an organic phase derived from the neutralization of the reaction mixture with a caustic soda solution. However, according to this process, the quality of the resultant p,p'-BPA is poor and a hydrogen chloride catalyst cannot be reused upon circulation.
Furthermore, many proposals relating to the use of acidic ion exchange resins or the modified products thereof as a catalyst during the reaction of phenol and acetone and the purification and separation of p,p'-BPA from the reaction product so obtained are disclosed in, for example, Japanese Examined Patent Publication Nos. 36-23334, 37-14721, 37-981, 41-4454, 45-10337, 46-19953, 48-71389, and 49-48319 and Japanese Unexamined Patent Publication Nos. 52-42861, 54-19951, and 54-19952.
However, in order to sufficiently effect the desired catalytic activity in the proposed processes, it is required that the concentration of p,p'-BPA.PhOH in the reaction system be maintained to a low level so as not to crystallize the p,p'-BPA.PhOH as a crystal to form a reaction mixture slurry and so as to form a homogeneous reaction mixture solution. For this reason, it is necessary to maintain the conversion of the starting acetone to 55 mole % or less or to increase the mole ratio of the phenol to the acetone in the reaction system. Accordingly, the one-pass conversions of the starting materials are low commonly in these proposed methods and, therefore, large amounts of the starting materials should be recovered from the reaction mixture and recycled to the reaction system. Thus, expensive utility costs are required for recovering and recycling the unreacted starting materials and, therefore, the desired effective and economical reaction cannot be carried out.
In addition, larger amounts of various isomer by-products, high-boiling point by-products, and colored by-products are also formed in addition to the desired p,p'-BPA in the reaction utilizing, as a catalyst, an acidic ion exchange resin, as in the case of the above-mentioned hydrogen chloride or hydrochloric acid catalyst. Various attempts to increase the yield of the desired p,p'-BPA by isomerizing the by-products to p,p'-BPA have also been proposed in these reaction processes utilizing acidic ion exchange resin catalysts.
For this purpose, for example, Japanese Examined Patent Publication No. 37-981 discloses the recycling of the remaining by-products, together with phenol and acetone, to a reactor containing the above-mentioned acidic ion exchange resin catalyst, after recovering p,p'-BPA or p,p'-BPA.PhOH and the unreacted starting materials from the reaction mixture. This patent publication also discloses that p,p'-BPA.PhOH is crystallized by cooling the resultant mixture obtained by distilling off the unreacted starting materials from the reaction mixture and, then, the reaction mother liquor containing the above-mentioned by-products after filtering-off the crystalline is recycled to the reaction mixture.
However, when the continuous reaction is carried out by circulating the reaction mother liquor containing the by-products to the reactor according to the disclosed process, the disadvantages of the above-mentioned processes utilizing the acidic ion exchange resin catalysts cannot be eliminated. Moreover, the by-products are accumulated in the reaction system due to low isomerization rate of the by-products in the reaction mother liquor to p,p'-BPA and, therefore, not only is the occurrence of the smooth reaction impaired, but also the desired p,p'-BPA having a high quality cannot be obtained. In addition, when a long-term continuous reaction is carried out, this phenomenon further becomes remarkable because the activity of the acidic ion exchange resin catalyst is remarkably decreased. Accordingly, this process is not advantageous for commercial production of p,p'-BPA.